The invention is directed to a process for the purification of the reaction mixture formed in the production of 2,3-epoxypropyltrialkylammonium chlorides by the treatment of chlorohydroxypropyltrialkylammonium chlorides with alkaline acting materials in aqueous medium. The 2,3-epoxypropyltrialkylammonium chlorides for example, serve as etherifying agents for the production of cationic starch ethers. The 2,3-epoxypropyltrialkylammonium chlorides are needed in high purity particularly for this purpose. They should be free both from materials which cause side reactions and, for example, lead to cross-linking of the starch and also from materials which contaminate the starch ether in undesired manner and allow it to be separated from these materials only with considerable expense.
It is known to produce 2,3-epoxypropyltrialkylammonium salts by reaction of epihalohydrins with trialkylamines in aqueous medium and then to purify the reaction mixture by extraction or by evaporation (distillation) under reduced pressure (Paschall U.S. Pat. No. 2,876,217, the entire disclosure of which is hereby incorporated by reference and relied upon). In these processes it has not been possible to obtain the 2,3-epoxypropyltrialkylammonium salt sufficiently free from impurities, especially from cross-linking acting materials.
It is also known to carry out the reaction of the epichlorohydrin with the trialkylamines in anhydrous organic solvents, such as 1,2-dichloroethane, and to recover the 2,3-epoxypropyltrialkylammonium salt formed by crystallization from the reaction mixture (German patent 2,056,002). In this process indeed there is obtained the 2,3-epoxypropyltrialkylammonium salt in relatively pure form. However, the process is very expensive, especially long reaction times are necessary.
Besides it is known to produce 2,3-epoxypropyltrialkylammonium salts by treatment of halohydroxypropyltrialkylammonium salts with aqueous alkali, such as sodium hydroxide, and to recover the 2,3-epoxypropyltrialkylammonium salt from the reaction mixture by evaporating this to a syrup, taking the syrup up with alcohol and crystallizing the 2,3-epoxypropyltrialkylammonium salt from the alcoholic (or alcohol-acetone) medium (German AS 2055046). Therewith to obtain the epoxypropyltrialkylammonium salt in sufficient purity, several recrystallizations are necessary. The process is cumbersome and unsuited for use on an industrial scale.